One standout performance can carry a movie, and Michelle Williams makes My Week with Marilyn worth the while.

Marilyn Monroe is forever immortalized as a 20th century American sex symbol, but outside of the late actress/singer/model’s most devoted circle of worshipers, many people only know the image of Marilyn, rather than the complicated realities of the woman behind the persona.

 My Week with Marilyn attempts to pull back the curtain and offer a more intimate look at the woman (rather than the icon) who was Marilyn Monroe – but is this exploration of a small moment in Monroe’s brief-but-epic lifetime enough to carry a movie? And is star Michelle Williams (Blue Valentine) able to convey both the public and private sides of Marilyn in a way that is captivating and interesting?

The film is an adaption of late writer Colin Clark’s books “My Week with Marilyn” and “The Prince, the Showgirl and Me,” which chronicled his own supposed encounter with Monroe during the production of Sir Laurence Olivier’s 1957 film, The Prince and the Showgirl. Like the source material that inspired it, My Week with Marilyn is told from Clark’s perspective, starting from when he was a young man from a prestigious English family, venturing out into the world to make his way. Colin (played by Black Death star Eddie Redmayne) is enamored with the notion of the motion picture business, so he boldly crashes the doors of Laurence Olivier’s production company, refusing to take “no” for an answer, until he finally proves himself worthy to the esteemed actor (deftly played by Kenneth Branagh) and lands himself a job.

As fortune would have it, Colin’s first gig is serving as third assistant director (read: errand boy) on Olivier’s new film, which stars none other than Marilyn Monroe (Williams). Colin is as starry-eyed as everyone else when Monroe first arrives – but that allure is quickly extinguished for many of the cast and crew (especially Olivier), as it becomes apparent that Marilyn is highly eccentric, unstable, unreliable, and generally difficult to work with. Colin, however, still loves the beauty queen, no matter how damaged she may be.

Thanks to some chance happenings, Colin eventually makes it onto Marilyn’s radar and becomes her close confidant and supporter. But as Marilyn’s manager, Milton Greene (Dominic Cooper), warns the young man at one point: picking up and discarding men like play things is what Marilyn Monroe does best.

Eddie Redmayne in ‘My Week with Marilyn’

Even though My Week with Marilyn boasts a cast of highly talented performers playing some iconic celebrities – Branagh as Olivier, Julia Ormond as his wife/stage actress Vivien Leigh, Dougray Scott as American playwright Arthur Miller, Judy Dench as elderly starlet Dame Sybil Thorndike (to name but a few) – by and large, the film is a standard, by-the-numbers memoir. There are also many traces of screenwriter Adrian Hodges’ extensive TV experience noticeable in the almost episodic way the film hops from moment to moment, with the only real connective tissue being Colin’s (at times contrived) observations and narration. The film offers little depth or thematic richness, other than to remind us that Marilyn Monroe was a complicated lady.

Similarly, longtime TV director Simon Curtis manages this big-screen project with a competent hand, and arguably makes art out of the film’s standout section (involving Marilyn and Colin’s stolen day together). It’s a sequence of surreally beautiful filmmaking, with the two leads framed in natural light against plush English landscapes (shots that Terrence Malick would almost certainly applaud). Curtis also manages to faithfully recreate some of the more iconic moments from The Prince and the Showgirl – but other than the nods to history, and some brief moments of visual art, the style and structure of the film are pretty standard as well.

What elevates My Week with Marilyn above the average memoir film, however, is the performance of Michelle Williams, who continues to quietly and succinctly prove that she is one of the best actresses of her generation. Williams accomplishes what few could hope to: she is able to emulate the onscreen radiance and star power of Marilyn Monroe during those movie-in-movie recreations of The Prince and the Showgirl. From appearance to attitude to mannerisms, it’s easy to buy Williams as a world-renowned sex symbol.

Michelle Williams as Marilyn Monroe

In the moments when Marilyn is not in front of the cameras, Williams digs even deeper and gives us a woman who is, at any given moment, a volatile combination of glamour, vulnerability and impenetrable mystery. It’s hard to be certain what is truly going behind those big eyes and that perfect smile; whether Marilyn’s “dumb blonde” persona is just the cover for a cunning manipulator, an insecure wreck – fame’s whore, its prisoner, or perhaps some alternating combination of all these things. Marilyn ultimately disappears from the film leaving behind as many questions as insights; it’s what simultaneously makes Williams’ performance so great, but the film as a whole only slightly above average.

As stated, My Week with Marilyn succeeds only in reminding us that behind the veil of celebrity are people as complicated as any of us. While it is a good notion to remember, it doesn’t really make for much of a rich, informative or wholly satisfying cinematic experience.  The moments where Williams is front and center onscreen are something special; when she is offscreen, and the focus turns to the Colin or the other supporting character and subplots, the film quickly loses steam.

Thankfully, one standout performance can carry a movie, and Michelle Williams makes My Week with Marilyn worth the while.

My Week with Marilyn is currently playing in theaters.